The measurement of total organic carbon (TOC) is frequently performed in environmental, clinical, and industrial settings. Current techniques require hazardous reagents, such as strong acid and oxidizing agents, ultraviolet light, or high temperature ovens, to carry out the oxidation reactions. The development of a safe and cost-effective electrochemical device capable of oxidizing organic carbon and determining TOC in aqueous solution would represent a significant advance in the art.
The concept of electrochemically oxidizing organics was demonstrated in the early 1990's as a technology for incineration of toxic organic industrial wastes. Unfortunately, this technology has thus far proven inefficient and of limited use. Over the years, a variety of working electrodes for electrochemically oxidizing organic carbon have been developed. The properties of a working electrode in an electrochemical cell is critically important since the working electrode is directly involved in the oxidation of the organic molecule. The most common working electrode material has typically been carbon-based or made from metals such as platinum, silver, gold, mercury, or nickel. Such electrodes, however, poorly oxidize because of their limited anodic range. These electrodes eventually themselves become oxidized, and therefore are inefficient for any practical use. To overcome these limitations, recent attention has focused on the potential use of diamond-film electrodes. Such electrodes are composed of a substrate material, such as silicon or titanium, coated with diamond. Such electrodes are made conductive by doping the diamond film with a conductivity inducing material which promotes p-type semiconductivity to almost metallic levels (e.g., boron).
The unique properties of highly boron-doped diamond (BDD) films include: i) low and stable voltammetric and amperometric background currents, ii) wide working potential window in electrolyte solutions, iii) reversible to quasi-reversible electron transfer kinetics for redox species, iv) morphological and microstructural stability at extreme anodic and cathodic potentials, v) low adsorption of polar molecules, and vi) long-term response stability. Recently it has been reported that BDD films have been coated on several substrates and used to replace earlier electrodes (e.g., gold or platinum) for substrates for electrochemical oxidation of organic wastes. In these uses, the BDD-film electrodes have been reported to be highly robust, capable of withstanding high anodic potentials, and resistant to self-oxidation. An example is the use of a BDD-film electrode for the electrochemical oxidation of phenol. Cyclic voltammetry showed that phenol, one of the most difficult organic molecules to oxidize electrochemically, was oxidized by a BDD-film electrode with no visible oxidation of the electrode itself, even after multiple cycles.